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AdvancedPublished 2026-07-02

EtherChannel Consistency: Repair a Mode Mismatch

Bundle lab

Advanced CCNP troubleshooting lab: a pair of Layer-2 switches are connected by a two-link EtherChannel intended to carry VLAN 90 between access hosts. The starter configuration ships broken on purpose: the inter-switch bundle won’t form due to incompatible aggregation modes, and a trunk allow-list drift on one side prunes VLAN 90. Diagnose with IOS show commands, correct the EtherChannel mode so LACP forms the Port-channel, and restore trunk policy so same-VLAN hosts can communicate.

Track
Est. time
45 minutes
Difficulty
Advanced
Topics

Learning objectives

  • Identify EtherChannel bundling failures using show etherchannel summary and show etherchannel detail.
  • Determine and correct an aggregation mode incompatibility so both member links bundle via LACP.
  • Validate and fix trunk policy so the required VLAN is transported end-to-end.
  • Confirm same-VLAN host reachability and interpret LACP neighbor and bundle flags.

Troubleshooting focus

  • Correlate member interface states and flags (suspended/standalone vs bundled) with the Port-channel state.
  • Compare EtherChannel protocol and mode on both ends; incompatible pairs will not bundle.
  • Inspect trunk mode, native VLAN, and allowed VLAN lists on the Port-channel to ensure the intended VLAN is transported.
  • Use host-to-host pings in the user VLAN to confirm forwarding after each fix.

Topology

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Grade your work

How this lab is graded
  • Build it your way. Where a lab lets you choose a value — a VLAN name, an interface description — grading checks that you configured it, not which name you picked. Names that another line has to reference, like an ACL applied with access-class, are stated in the guide and do have to match.
  • Addresses, modes and protocol keywords are exact. An IP address, a subnet mask, switchport mode trunk, an encapsulation — these carry the meaning of the lab, so they are graded as written in the guide.
  • Grading reads your saved configuration. Export the lab from CML after you have configured it, and make sure anything you set is in the running-config — a change that only exists in a terminal session never reaches the grader.
  • You can submit as many times as you like. Your best score stands, and each attempt tells you which checks passed so you can work the gaps.
  • Scored something you believe is correct? Use Report an issue on this page — that is exactly how the grading fixes in the changelog got found.

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